1. Field of the Invention
The present invention concerns a pressure plate for mines, in particular anti-tank mines.
It also concerns a mine comprising a pressure plate of this kind.
2. Description of the prior art
A mine of this kind comprises an operational pyrotechnic charge enclosed in an enveloping body having in its upper part a so-called "pressure plate" adapted, when it is completely depressed, to release a striker which initiaes an ignitor pyrotechnic charge for the operational pyrotechnic charge.
Mines of this kind are described, for example, in French patents Nos. 2 357 860 and 2 504 254 in the name of the assignees of the present applicants.
In this instance the pressure plate cooperates with a countermeasures hydraulic circuit comprising a pressure chamber containing a fluid that is compressed by the force exerted on the plate and evacuated in a controled manner by a depressurization unit, such as a calibrated orifice, for example, in response to a sustained force exceeding a predetermined threshold being applied to the plate.
The depressurization unit thus slows down the depression of the plate so that complete depression of it will always require a sustained force to be applied to it for a certain time interval, exceeding the duration of the blast from an explosion but less than the time taken for a track roller of a moving tank to pass over it.
Although a device of this kind constitutes an effective countermeasure against explosive methods of mine clearing ("anti-blast" countermeasure) it is nevertheless ineffective against other mine clearing techniques that may be employed to open up a breach in a minefield, especially use of a tank fitted with a mine clearing roller: the force exerted by the roller on the pressure plate is in all respects comparable with that exerted by a tank track roller and conventional mines do not currently incorporate any countermeasure to this type of operation.
One objective of the invention is to propose a new countermeasure device for mine pressure plates whereby the mine is triggered not in response to an initial sustained force applied to the plate (which could correspond to a mine clearing roller passing over it) but only to a second sustained force sensed by the pressure plate.
This type of countermeasure has the further advantage of delaying triggering of the mine, when a tank passes directly over it, until the second roller passes over the mine; this contributes to enhancing the destructive effect of the mine.